The availability of optical systems that dazzle or blind an equipment operator, guide a beam-following vehicle to an equipment platform, or laser-pinpoint an object of interest, represent a threat to manned and unmanned apparatus. Ultimately, a technology is required that can perform these functions:                1. separate lasers from false-alarm light sources (natural or manmade)        2. determine the wavelength of the laser        3. determine the location of the laser threat        4. determine the pertinent laser event temporal and power characteristics for both CW and pulsed lasers        5. cover a wide dynamic range of laser powers, sensitive to energy levels many orders of magnitude lower than those which are dangerous to vision.        
Conventional Detection Systems
Current laser-warning receivers are principally based on detecting where light falls on a focal plane located behind a large field-of-view (FOV) optic. These systems are relatively slow in their response, and relatively inaccurate in terms of their line-of-sight (LOS) measurement of the location of the incoming laser beam.
In addition, they are relatively bulky and heavy. Further, existing laser-detection and -warning receivers provide little if any spectral information.
Examples are the present laser-detection systems built by companies such as BAE systems and Goodrich, particularly the AN/AVR-2 Laser Detection Set 112 (FIG. 1). They are bulky (not compatible with installation in an aircraft cockpit), highly inaccurate in terms of determining location of a laser-beam source, and yield no spectral information for the incoming beam.
Companies such as Princeton Scientific Instruments have developed smaller laser-detection packages 113 that are compatible with implementation in a small aircraft. Again, however, these provide no directional or spectral information, and can only detect average irradiance levels as low as 10−11 W/cm2.
Components not Previously Associated with Laser Warning (Except in Our Own Work)
One such device is a four-sector detector or quadrant detector, familiarly called a “quad cell”. Prior to mention in some of the Kane documents listed above, quad cells to the best or our knowledge were not used in laser-warning systems but rather were known primarily for light-beam position control in industrial machinery.
In one of those earlier documents, the quad cell was said to be inferior to a so-called “position-sensing detector” (PSD). A quad cell is a detector with four discrete photosensitive sectors arranged within a circular overall detection array, with corners of each of the four sectors mutually adjoining at the center of the circle.
Independent detection-signal leads from the four discrete sensing areas are brought out separately to independent circuitry, enabling detection and particularly quantitative comparison of light levels incident on the four sectors. Conventionally such comparison is used simply to find ratios of the radiant powers reaching the different sectors.
Such ratios are assumed to be due to distribution of light from a single common source, on the overall detector surface. Based on that assumption, such ratios are conventionally used to directly calculate direction of origin of the light.
To facilitate that kind of operation, conventional systems defocus the incident light spot so that it spans, speaking very roughly, about one-third or more of the overall sensor diameter. The rationale is to provide that at least some of the light will strike each one of the four sectors—thus enabling routine ratioing operation based upon the assumption that none of the sectors receives zero light.
Quad cell response is very fast, but the pointing accuracy of such a conventional system is quite poor—particularly in a low-light-level environment. This is because signal-to-noise properties of such operation are distinctly unfavorable in comparison with those of, e.g., a PSD also as conventionally used.
Quad cells heretofore have been used in passive sensing systems exclusively. Thus we are not aware of any prior usage of a quad cell in a system which emits a probe flash and then analyzes reflected return.
Another component previously unknown in laser-warning systems, except our own earlier development efforts, is an array of one or more very small mirrors, particularly microelectromechanical systems (“MEMS”) mirrors. The first significant commercial use of such mirrors was the Texas Instrument Digital Light Projector (DLP) MEMS array.
Formed in an array of 1,000-by-1,000 two-axis 10 μm mirrors, the bi-stable mirrors were controlled open-loop, with the mirrors stepped from ±10° locations at rates on the order of 10 ms. The mirrors were not analog—more specifically, each one could only take on one of two positions about either axis—and were not particularly useful from a wavefront-correction perspective.
A more closely related development in MEMS scan-mirror arrays was in the area of optical switching, where the mirrors could be controlled open-loop about one or two axes over the entire range of mirror travel, and thus were “analog” in the sense of being able to point the mirrors. Lucent in its “Waverunner” optical switch, and Calient Networks, with its “3-D” MEMS-mirror optical switch, are good examples of this technology.
These arrays are typically larger, from millimeters to hundreds of millimeters, but have millisecond-level step-response characteristics because they are controlled open-loop. Areal densities of these arrays are also low, less than fifty percent; therefore significant modifications to their architecture are required to obtain an adequate array for an AMBS-quad system.
Conclusion
Accordingly the prior art has continued to impede achievement of uniformly excellent laser-alert equipment, and in particular has failed to make use of quad-cell and MEMS technologies to enhance laser-alert capabilities. Thus important aspects of the technology used in the field of the invention remain amenable to useful refinement.